Impacts of Large Dams: A Global Assessment

For nearly 5,000 years, water-retaining structures have been built in different parts of the world to ensure water is available for domestic and agricultural purposes throughout the year. From time immemorial, human beings have settled in the fertile plains of major rivers like the Nile in Africa, Euphrates-Tigris in Mesopotamia, and the Indo-Gangetic plain in the Indian subcontinent. In these areas, floods and droughts had to be managed to reduce losses to human and cattle populations and also to limit economic damage. During the past two centuries, hundreds of millions of people lived around rivers, which necessitated control of these rivers to provide assured water supply for domestic, agricultural and industrial purposes and to reduce flood and drought damages. Thus, the building of dams has gained steady momentum. More recently, after the 1930s, water requirements increased exponentially in countries where there was significant immigration, such as Argentina, Australia, Brazil, Canada and the United States, to satisfy the needs of their expanding populations. Globally, with the passage of time, water control and assured availability of water of appropriate quality became essential requirements for continuing economic and social development.

Dam projects generate a vast array of economic impacts—both in the region where they are located, and at inter-regional, national and even global levels. These impacts are generally evaluated in terms of additional output of agricultural commodities, hydropower, navigation, fishing, tourism, recreation, prevention of droughts and reduction in flood damages, and are referred to as direct impacts.

The adverse social impacts of most large dams continue to be unacceptable. They also reduce a project’s potential benefits. This is especially the case with resettlement which some experts (including Asit Biswas and Robert Goodland, former Chief Environmental Adviser of the World Bank Group) consider to be the most contentious issue associated with large dams. Fortunately, there is potential for helping resettling communities to become project beneficiaries.

It is difficult to conceive of another aspect of water resources development that evokes as much emotion, public concern and challenge for policy makers as dam and reservoir construction. Some want to store water, generate electricity, irrigate or ameliorate living in other ways by constructing dams. Others oppose this because dams and reservoirs destruct valuable ecosystems, displace people from river valleys where they have dwelled for millennia and so on.

In Switzerland, most dams are built to create reservoirs for the production of hydropower, some for seasonal and some for weekly or daily compensation between the pattern of run-off and that of electricity demand, respectively. Only a very small number of dams have been built for flood retention, even though, in fact, many of them are playing that role. Unlike the situation in most other countries, especially in dry areas, almost no dams in Switzerland are used for irrigation. The annual distribution of rainfall allows for agriculture without any significant irrigation and, if the necessity arises, water is taken directly from the rivers, which generally have enough run-off even in periods when there are agricultural requirements for water.

Until quite recently population displacement due to hydrodevelopment was very rare in Argentina and not a very important topic for public discussion. However, the construction in the last decades of some large projects as well as the increasing sophistication and power of ecologist movements led to a new prominence of this topic in public conscience and the mass media. The result was a strong movement ‘against’ large dams and its plethora of ecological and social consequences.

Brazil is a large country with an area of 8.5 million km² and a population of approximately 184 million in the year 2008. The country is rich in water resources, with the impressive rank of holding 14% of the world’s waters. This large amount of water is unevenly distributed in time and space across the territory. The northern region of the country accounts for 68% of the total available water in the country while the semi-arid northeast region faces severe water shortages. The population distribution is also diverse. The northern region, where most water is available, is home to only 7.6% of the population. The northeast, with only 3% of the country’s water, is inhabited by 30% of the population. The semi-arid climate of this region has very irregular annual average rainfall, ranging from 200 to 700 mm, and its population is the poorest in Brazil, facing serious social problems. The few humid areas of this region are limited to those bordering the northern region and the coastal strip. Its high climatic variability has led to the construction of dams to regulate flows, thus providing water supply and irrigation for food production. The construction of these dams and reservoirs was responsible for a significant increase in the social and economic development of this region.

The Southeastern Anatolia Region of Turkey has historically been a plateau with low productivity. Although rich in water, land and human resources, the region has lagged behind the rest of the country in terms of development. The development potential of both the Euphrates and Tigris Rivers was recognised in the 1960s, and the idea of harnessing their waters for irrigation and hydropower generation emerged.

The King River Power Development, on the rugged west coast of Tasmania, is a good example of excellence in hydroelectric power development, and in many ways provides a guide for the overall development and sustainable operation of other hydroelectric power schemes. The scheme demonstrates sustainable environmental and economic development, and has noteworthy technical innovations. It was developed and is owned, operated and maintained by Hydro Tasmania.

In the past 56 years, China has seen more than 70 million involuntary resettlers due to its large-scale economic growth, including the construction of reservoirs, railways, roads, power plants and power transmission projects, airports, watercourses, urban water supply and sewage treatment projects, urbanisation and reconstruction and land acquisition for development and real estate.

In China one speaks not of dams and their heights but of reservoirs (shuiku) and their capacities. Beijing claims to have over 80 large reservoirs (storage capacity over 0.1 km³), but the municipality’s surface water systems are dominated by two: the Guanting (capable of many literal translations into English, but perhaps most closely, ‘Officials’ Office’), controlling over 90% of the Yongding River catchment in the west, and the Miyun (‘Dense Clouds’) controlling 88% of the Chaobai River catchment in the northeast.

Water resources have to be developed to overcome their spatial and temporal variability and availability, particularly for countries in the tropics. To this end, India, like other developing countries, launched a massive programme after independence to build storages on its large rivers and soon attained the required degree of development from its potential for development. However, resistance to the building of new dams emerged over time due to the perceived neglect of adequate resettlement and rehabilitation for the displaced.

Water is the most vital element that supports life. It is also the prime mover of economic development and symbolises survival, growth and prosperity, so much so that it has long been the focus of attention and the centre of all future planning and strategy. Over the centuries, however, it became clear that in order to attain the objective of overall development there was a need for large dams or, for that matter, large multi-purpose projects, to spread benefits widely, which were strictly localised in earlier times. In post-independence India, several dams and multi-purpose projects have been constructed to increase food production, energy generation, drinking water supply, fisheries development, employment generation, etc. In the long run, most of these projects have not only been successful in delivering the benefits that were expected prior to their construction, but over the years, they have radically transformed the economic scenario of their command areas. In spite of this, for the last decade or so, there has been a scathing attack on the feasibility of large dams within the domain of ‘development’. Numerous questions have been raised, ranging from environmental to ecological and social issues, some of which are rather trivial and seem deliberately posed to create confusion among the masses (notwithstanding the fact that most people have been direct beneficiaries of those large projects).

The Golden Jubilee of the successful operation of the Bhakra-Nangal Project was celebrated in July 2004. This multipurpose project has been in the service of the Indian Nation for the last five decades and has yielded immense benefits, far beyond expectations. At the opening ceremony of the Nangal Hydel Channel on 8 July 1954, India’s first Prime Minister Jawaharlal Nehru made a speech at Nangal and paid tribute to the good work done by the project.

The Koyna Dam, which was built across and is named after the river Koyna, was undertaken for the primary purpose of hydropower generation by Maharashtra state as part of the upsurge in nation building activities after India’s independence. The dam has become a symbol of achievements in water resources development during the last five decades. It is the upstream most dam in the Krishna River Basin, 103 m in height, storing close to 2.8 billion cubic metres (BCM) of water in a reservoir with a spread of over 115 km², near the Sahyadri Range which serves as a Continental Divide that is over 1000 m high at the head of the major peninsular Krishna River Basin.

India is one of the few developing countries in the world with a sizeable number of dams. The building of dams is still ongoing in as much as the storage per capita is far below requirements, especially when we consider the temporal and spatial variations in the pattern of rainfall, and the arid and semi-arid areas of large parts of India. The per capita energy availability is also far below the minimum need. Thus, notwithstanding the new emphasis on ‘management’ and ‘efficiency improvement’ of existing assets, the creation of additional and new storage through dams is an absolute necessity.